1. Field of the Invention
Farm, off-highway construction equipment and industrial tractors, especially those units employing a common fluid reservoir, presently use multifunctional lubricants. These lubricants are considered multifunctional because they must meet the requirements of the transmissions, differentials, final drives, hydrostatic transmissions, hydraulic systems, power steering systems, and fluid immersed disk brakes of the specialized equipment. Thus, for a lubricant to be considered for use in such equipment, it should desirably contain the following properties: oxidative and hydrolytic stability, good antiwear qualities, and compatibility with other lubricant compositions.
In addition, friction modifying characteristics are very important to assure proper, decisive operation of multi-disc transmission clutches and oil immersed brake discs. Water tolerance characteristics are especially important in friction modified lubricants for maintaining the performance integrity of the lubricant in the presence of water formed or introduced during operation.
This invention relates to lubricant compositions, which may be in the form of fuels, heat exchange fluids, lubricating oils or greases thereof, which possess improved water tolerance, friction modifying, antiwear, and antichatter properties. Such compositions are contemplated as being suitable for use in the specilized equipment described hereinabove.
2. Description of the Prior Art
British Pat. No. 1,247,541 discloses lubricant compositions containing alkanephosphonates as having friction modifying characteristics. The alkanephosphonates described therein have the formula: ##STR3## where R is methyl or ethyl, R' is a straight chain alkyl having 12 to 20 carbon atoms and X is a methyl, ammonium, alkylammonium or alkenylammonium group, the organic X group having from 1 to 30 carbon atoms. These compounds may be produced as follows: ##STR4## where R and R' are defined above and, R" and R'" are each alkyl or alkenyl of 1 to 30 carbon atoms.
In reaction (1), a dialkyl phosphonate is reacted with an olefin to produce a R' substituted dialkyl phosphonate. This product is partially hydrolyzed in step (2) by treatment with a base followed by acidification to produce an R' substituted monoalkyl acid phosphonate, which may be further reacted with an amine to form the corresponding salt by acid-base neutralization reaction (3 ) with a transfer of the acid hydrogen. An acid-base neutralization reaction involving a proton transfer, for example: HA + R.sub.2 NH .revreaction. A.sup.- + R.sub.2 N+H.sub.2 is reversible. If the equilibrium is destroyed such as by distillation of the acid or amine, the original reactants can be recovered. Due to the reverisibility of reaction (3) the salt products of the British patent may actually contain some acid phosphonate. Such compounds are sources of "reverse" acidity and tend to "deactivate" basic components of lubricant compositions by neutralization. It is further noted that the hydrolysis and acidification reactions of step (2) are very corrosive and, in addition, present problems with regard to emulsions, exotherms, solvents, solvent recovery, and comprise a multistep process.
In U.S. Pat. No. 3,793,199 an alkanephosphonate diester is reacted with a non-cyclic amine at temperatures of from 80.degree. to 150.degree. C, with 90-130.degree. C being preferred, according to the following formula: ##STR5## where R is a substantially straight chain aliphatic radical having from about 11 to 40 carbon atoms, R' is a lower aliphatic radical having from one to eight carbon atoms, R.sup.2 is a hydrocarbyl radical having from one to 40 carbon atoms and R.sup.3 and R.sup.4 are hydrogen, a hydrocarbyl radical having from one to 40 carbon atoms or a substituted hydrocarbyl radical having amino, alkylamino or hydroxy functional groups.
When R.sup.3 and R.sup.4 are hydrogen, a reversible acid-base reaction may occur. For example, if R.sub.3 were hydrogen, the following reverisble acid-base type reaction: ##STR6## would cause the production of acid phosphonate. The detrimental effect of the presence of acid phosphonate in a lubricant composition has already been discussed.
In South African Pat. No. 74/4882, there is described a lubricant composition which contains a salt of (a) an amine or an imidazoline which contains a straight chain aliphatic group of 12 to 22 carbon atoms and (b) an alkyl, long chain alkyl (C.sub.12 - C.sub.22) acid phosphonate.
It is noted that none of the products described in the prior art were formed by the reaction of a dialkyl alkanephosphonate, substituted imidazoline and water.